A pneumatically actuated telescoping mast is well known in the prior art and is generally of such a nature that it may be mounted readily on the roof of a vehicle. In such arrangement the mast is generally used for positioning electrical devices, particularly emergency lighting fixtures, and an elevated point above the vehicle. The effect is to immediately light a large area about the vehicle in order that emergency procedures can be conducted. Pneumatically actuated telescoping masts are particularly advantageous in such situations since they are light weight, compact in a retracted position and capable of being mounted on the roof of most emergency vehicles, including automobiles.
Pneumatically actuated telescoping masts have the further advantage of having full, open and unobstructed mast sections. These sections permit electrical wiring to pass within and through the telescopic tubular mast sections for controlling electrical devices or fixtures mounted on the mast. The electrical wiring does not interfere with or affect the pneumatic system or the air pressure required to extend and retract the mast. Thus, the electrical portions and component parts are completely housed within the mast and protected from the weather elements. Other problems associated with the storage and reeling out of external wire which is connected to the mast are also eliminated. The prior art pneumatically telescoping masts are extended using air under pressure and, in a fully extended position, are necessarily vertical. Pneumatically telescoping masts heretofore available are not capable of being maintained at a plurality of angles between a horizontal and vertical position. Indeed, the pneumatic masts have only two fixed positions, horizontal and vertical as seen in Featherstone U.S. Pat. No. 4,413,451. The pneumatic system used to inflate the mast in Featherstone is also used to pivot the mast between horizontal and vertical positions.
The pneumatic telescoping mast is specifically advantageous for use in emergency situations. The light weight feature enables the telescoping mast to be mounted on an emergency vehicle or automobile. However, the users of such pneumatic telescoping masts have long desired more versatility in the placement of a light at the top of the mast relative to the work area to be lighted. Police and other emergency personnel have realized that the existing light mounted on pneumatically telescopic mast would be more useful if it could be inclined relative to vertical and placed directly over the site to be lighted, instead of adjacent thereto. This would eliminate the problem of shadows cast by objects or people coming between the area desired to be lighted and the vehicle. Such shadows hinder the work of emergency personnel. For example, in certain situations, an emergency vehicle cannot immediately access an emergency site. In such situations, it would be advantageous to incline the light at an angle to the vehicle in order that the light beam can be directly placed over the emergency site. Due to the pneumatic telescoping feature, it has not been possible heretofore to place a pneumatic mast at a desired tilt angle in order to place a light or electrical receptacle mounted on the outer end of the mast directly over the emergency site where it is most needed. Such a tiltable pneumatic telescoping mast would be very desirable during rescue of persons in areas which are difficult to reach with an emergency vehicle, such as in a body of water, under a bridge or over the edge of a ravine.
Previous attempts at developing a tilt mechanism for a pneumatically telescoping mast have not proved successful. These attempts include a screw drive mechanism utilizing a ball nut and screw to manipulate the mast and thus the angle of the mast relative to the vehicle on which it is mounted. A screw drive mechanism adds a significant amount of weight to the roof of the vehicle and screw drive mechanisms are expensive and prone to malfunction. A screw drive mechanism is also subject to differing torque loads as the mast is raised and lowered. This also increases the wear on the screw drive, and thus the device requires frequent maintenance. Finally, some screw drive arrangements are structurally complex and thus more expensive and especially hard to repair, and usually require replacement as opposed to maintenance.
An alternative to a screw drive mechanism is a hydraulic system. While less expensive to maintain, the upfront capital costs of hydraulics add greatly to the overall costs of a pneumatic telescoping mast. Additionally, hydraulics, and their associated fluids add significant weight to the telescoping mast system. Finally, hydraulics also require a separate pressure and fluid flow system distinct from the air system used to inflate the mast. The dual systems which would be required would significantly add to the cost of a telescoping mast.
Both the screw drive mechanism and hydraulic system require additional space adjacent the telescoping mast. However, the dimensions of an emergency vehicle roof are not always large enough to accommodate a pneumatic mast with the aforementioned tilting mechanisms. The light bar atop an emergency vehicle presents additional clearance problems, and can further restrict the space available.